1. Field of the Invention
The present invention relates to a magnetoresistive element composed of a pinned layer, a non-magnetic layer, and a free layer deposited in stacked relation, to a magnetoresistive head comprising the magnetoresistive element, and to respective methods for fabricating the magnetoresistive element and the magnetoresistive head.
2. Description of the Related Art
As magnetic disk apparatus have been increased in density, a high sensitivity read head has been on growing demand. As an example of the high sensitivity read head, a structure as disclosed in Non-Patent Document 1 has been known, in which two ferromagnetic layers are separated from each other by a non-magnetic metal layer and an exchange bias magnetic field is applied from an antiferromagnetic layer to one of the ferromagnetic layers to fix the magnetization thereof.
It is shown in the foregoing paper that, in such a multilayer film, a resistance R has a component which varies in proportion to cos θ as a function of an angle θ between the respective magnetizations of the two ferromagnetic layers. Such an effect is termed a giant magnetoresistive effect (GMR) or a spin valve effect and such a multilayer film is termed a magnetoresistive film.
There are cases where a sense current is caused to flow in parallel to a film surface (Current in plane, hereinafter referred to as CIP) and where the current is caused to flow perpendicularly to the film surface (Current perpendicular to the plane, hereinafter referred to as CPP) in the giant magnetoresistive head. It has been known that an MR ratio in the CPP mode is twice or more as high as the MR ratio in the CIP mode. Reports on the giant magnetoresistive head in the CPP mode are disclosed in, e.g., Patent Document 1 and Patent Document 2.
To obtain an excellent read voltage in these read heads, it is necessary to change the ferromagnetic layer composing the magnetoresistive film into a single domain. For this purpose, there is a magnetic domain control method termed a hard bias structure, which is disclosed in, e.g., Patent Document 3. The method suppresses Barkhausen noise resulting from a magnetic domain structure by disposing permanent magnetic films at both ends of the magnetoresistive film, applying a longitudinal bias field for magnetic domain control in a direction of track width to the magnetoresistive film, and thereby changing the ferromagnetic layer into a single domain.
As another method for changing the ferromagnetic layer into a single domain, a method for magnetic domain control termed patterned exchange is disclosed. in, e.g., Patent Document 4. The method disposes antiferromagnetic layers in left and right end regions in spaced apart relation such that they are in direct contact with the top portions of the ferromagnetic layer, thereby fixing the respective magnetizations of the both end regions of the ferromagnetic layer by exchange coupling to the antiferromagnetic layer and changing the ferromagnetic layer into a single domain. It is normally assumed that the magnetizations of the both end regions of the ferromagnetic layer are oriented in the direction of track width.
Patent Document 5 discloses a head having read sensitivity improved by tilting the magnetizations of the both end regions of the ferromagnetic layer from the direction of track width. In the head, the respective magnetizations of the left and right end portions are tilted in the same direction for improved read sensitivity.
FIG. 16 shows a conventional CIP mode giant magnetoresistive head to which magnetic domain control has been performed by patterned exchange. The head comprises a magnetoresistive film (GMR film) 30 composed of a free layer 35, a non-magnetic metal layer (Cu layer) 40, a pinned layer 45, and an antiferromagnetic layer 50 which have been stacked. The magnetization of the pinned layer 45 is fixed to the direction of element height of head. In general, an axis of easy magnetization for the free layer 35 is oriented to be parallel with the direction of track width of head.
To fabricate the CIP mode giant magnetoresistive head, a magnetic shield layer 10, a magnetic gap layer 20, and the magnetoresistive film (GMR film) 30 are deposited first on a substrate 5 in stacked relation. After an antiferromagnetic film 60 and an electrode film 70 are deposited on the magnetoresistive film 30, they are patterned. Then, a magnetic shield film 90 is formed on the electrode film 70 with a magnetic gap layer 80 interposed therebetween.
[Patent Document 1]
U.S. Pat. No. 5,668,688
[Patent Document 2]
Japanese Laid-Open Patent Publication No. 2000-228004
[Patent Document 3]
Japanese Laid-Open Patent Publication No. HEI 3-125311
[Patent Document 4]
U.S. Pat. No. 4,663,685
[Patent Document 5]
Japanese Laid-Open Patent Publication No. HEI 8-147631
[Non-Patent Document 1]
“Giant Magnetoresistive Effect in Soft Magnetic Multilayer Film” (Physical Review B, Vol. 43, pp,1297–1300)